Open AccessFactors affecting the determination of cerebrovascular reactivity
Author(s) -
Regan Rosemary E.,
Fisher Joseph A.,
Duffin James
Publication year - 2014
Publication title -
brain and behavior
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.915
H-Index - 41
ISSN - 2162-3279
DOI - 10.1002/brb3.275
Subject(s) - supine position , middle cerebral artery , blood pressure , cerebral blood flow , medicine , mean arterial pressure , cardiology , blood flow , confounding , sitting , anesthesia , heart rate , ischemia , pathology
Abstract Background and Purpose Cerebrovascular reactivity ( CVR ), measures the ability of the cerebrovasculature to respond to vasoactive stimuli such as CO 2 . CVR is often expressed as the ratio of cerebral blood flow change to CO 2 change. We examine several factors affecting this measurement: blood pressure, stimulus pattern, response analysis and subject position. Methods Step and ramp increases in CO 2 were implemented in nine subjects, seated and supine. Middle cerebral artery blood flow velocity ( MCA v), and mean arterial pressure ( MAP ) were determined breath‐by‐breath. Cerebrovascular conductance ( MCA c) was estimated as MCA v/ MAP . CVR was calculated from both the relative and absolute measures of MCA c and MCA v responses. Results MAP increased with CO 2 in some subjects so that relative CVR calculated from conductance responses were less than those calculated from CVR calculated from velocity responses. CVR measured from step responses were affected by the response dynamics, and were less than those calculated from CVR measured from ramp responses. Subject position did not affect CVR . Conclusions (1) MAP increases with CO 2 and acts as a confounding factor for CVR measurement; (2) CVR depends on the stimulus pattern used; (3) CVR did not differ from the sitting versus supine in these experiments; (4) CVR calculated from absolute changes of MCA v was less than that calculated from relative changes.